The present invention relates to a rotation angle sensor incorporating at least two resolvers, and in particular to a rotation angle sensor that detects the amount of relative rotation of an input axle and an output axle of, for example, an automobile power steering device that manipulate a steering device torsion bar as a result of their relative rotation.
A rotation angle sensor may be used in conjunction with a power steering device to detect a relative turning angle of an automobile steering wheel for steering control-related applications. Specifically, the sensor detects the amount of relative rotation of an input axle and an output axle arranged on the steering device torsion bar when resolvers respectively rotate the input axle and the output axle.
As shown in FIG. 5, a first resolver 101 in a conventional rotation angle sensor secures one end of a torsion bar 103 to the input axle (not shown), a second resolver 102 secures the other end to the output axle (not shown). When the power steering device (not shown) causes the input axle and the output axle to rotate, the torsion bar 103 is twisted, and the resolvers 101, 102 detect the amount of relative rotation of the input and output axles.
An input side cylindrical rotor 104 is fastened on the input axle side of the torsion bar 103, and an output side cylindrical rotor 105 is fastened on the output axle side. In addition, a housing 106 surrounds the circumference of both rotors 104, 105 as well as both stators (an exemplary stator 118 is shown in FIG. 6).
As shown in FIG. 6, the input side resolver 101 includes a first magnetic circuit with a ring-shaped first yoke 107 that is provided in the inner circumference of the housing 106 and a first coil 108 that is provided inside the first yoke 107. Furthermore, the first magnetic circuit also includes a ring-shaped second yoke 109 that faces the first yoke 107 and that is fastened on the outer circumference of the input side cylindrical rotor 104, and a second coil 110 that is provided within the ring-shaped second yoke 109.
The input side cylindrical rotor 104 also includes a third yoke 111 that is fastened on the circumference thereof, and a third coil 112 that is connected to the second coil 110 on the circumference of the third yoke 111, and that has two types of coils with respective phases shifted by 90°. The stator 118, which is provided on the inner circumference of the housing 106, includes a fourth yoke 113 and a fourth coil 114 that respectively face the third yoke 111 and third coil 112 of the input side cylindrical rotor 104. Similar to the third coil 112, the fourth coil 114 has two types of coils with respective phases shifted by 90°. Lead lines 115, which are connected to the first coil 108, and lead lines 116, which are connected to the fourth coil 114 of the stator 118, extend externally from the housing 106.
The output side resolver 102, which has the same structure as the above described input side resolver 101, is provided between the output side cylindrical rotor 105 and the housing 106.
Referring again to FIG. 5, the step 117 at the center portion of the rotation angle sensor in FIG. 5 spaces the resolvers 101, 102 apart from one another and acts as a stopper to limit the amount that the resolvers can be moved inwardly in an axial direction toward one another. Both of the lateral sides of the step 117 actually maintain the resolvers 101, 102 in their respective positions as shown.
Although the torsion angle of the torsion bar 103 is relatively small, the torsion bar 103 nonetheless rotates while in a torqued state. Therefore, the resolvers 101, 102 that are connected thereto are required to have a high detection precision relative to the entire circumference of the torsion bar 103. However, it has been difficult to realize such a high level of detection precision over the entire circumference of the torsion bar 103 with conventional rotation angle sensors.
The above-mentioned conventional rotation angle sensor has additional limitations. For example, it is difficult to manufacture, and it is difficult to connect the lead lines 115, 116 of the rotor and stator coils, such as the coils on which the detection signals are output to a processing control device (not shown). In addition, it is difficult to align the two resolvers 101, 102 in the housing 106, and to manufacture the housing 106 with the amount of precision that is required for the above application. Furthermore, whether the rotation angle sensor is non-defective or defective can be determined only after both resolvers 101, 102 are arranged in the stator 118.
In response to the above-mentioned limitations, resolver configurations such as the one shown in FIG. 7A provide first and second resin insulation caps 203, 204 on a ring-shaped steel core, or stator stack, 202 that includes stator windings 201. The term “axial direction” will refer to the lengthwise direction of a rotation shaft extending through the resolver.
The pins 205 project from the first insulation cap 203 and the printed circuit substrate 206a, which are arranged in parallel with, and on one side of, the second cap 204. The pins 205 are implanted by impact or insert molding into the second insulation cap 204. On each of these pins 205, the stator windings 201 are connected by the winding hook 207. The tip of each of the pins 205 and the wiring pattern of the printed circuit substrate 206a are connected by soldering. Therefore, the printed circuit substrate 206a is fastened to the stator windings 201 by the pins 205 so that it extends outwardly in the axial direction from the first insulation cap 203 in a floating manner. The wiring pattern of the printed circuit substrate 206a is connected to external signal output lines (not shown).
The first and second insulation caps 203, 204 are directly provided on the stator stack 202, and therefore are directly affected by heat generated by the stator 201. Further, the exemplary stator 201 in FIG. 7A is only a single stator. Therefore, if two stators such as the one shown in FIG. 7A are required, the stators have to be provided in parallel to conform to a housing such as the one shown in FIG. 5. In the single stator example of FIG. 7A, the end of the stator windings are hooked on the pins 205 provided on the circuit substrate 206a, and the pins 205 are wired to the external signal output lines 214 (FIG. 7C) through the printed circuit substrate 206a. Therefore, if two stators are implemented together, the stators must be connected to the external signal output lines 214 in a manner such as that shown in FIGS. 7B and 7C.
Specifically, the circuit substrate 206a, which is a signal relaying substrate for a first of the two stators 201, includes an L-shaped pin 211 soldered to a connecting substrate 213, which in turn is connected to the signal lines 214. Similarly, the circuit substrate 206b, which is the signal relaying substrate for a second of the two stators 201, includes an L-shaped pin 212 also soldered to the connecting substrate 213.
The housings required for the resolvers shown in FIGS. 5 and 7A–7C typically have several limitations. For example, because the housings are thin and relatively long, high production yield is difficult to achieve. In addition, inspection of the resulting rotation angle sensor for deformation caused by installation of the resolvers can be carried out only after both resolvers are installed in their respective housings. Therefore, if one of the two resolvers is defective, the other non-defective resolver is also not usable. Still further, when the two resolvers are aligned at their respective zero points within their respective housings, the resolvers have to be fastened during alignment of the two stator stacks, thereby increasing the complexity of assembly.
In addition, the hammering of the pins, such as the pins 205 in FIG. 7A, into the second insulation cap 204 often causes deformation or cracking of the insulator resin of the second insulation cap 204 or a deformation of the pins themselves. Also, as the temperature of the stator stack 202 increases, the pins 205 have a tendency to loosen from the second insulation cap 204 due to the expansion and softening of the insulation cap resin.
Still referring to FIGS. 7A–7C, because the circuit substrates 206a, 206b are formed from materials such as resin, the substrates have different thermal expansion coefficients than the pins 205. Therefore, when the circuit substrates 206a, 206b are connected to the stator windings using the pins 205, the stress due to thermal expansion and contraction that is repeatedly applied to the connecting junction tends to disconnect the pins 205 from the circuit substrates 206a,206b. 
While the floating structure of the circuit substrates 206a, 206b reduces the stress due to thermal expansion and contraction, such a structure does not completely remove the stress. In addition, alignment of the pins 205 is difficult. Therefore, to maintain the precision of the location of the pins 205, the precision of the elements and the installation precision have to be precisely controlled.
Therefore, what is needed is a multi-resolver rotation angle sensor that has a single integrated housing, an external signal output line connecting terminal that does not require terminal pins to be hammered therein, and a simplified wiring configuration that minimizes the effects of thermal stress on connection points between the resolver stator and stator wiring connections.